.box {
    width: 100%px;
    height: 800px;
    background-image: url(../images/xmy/bg1.jpg);
    background-size: 100% 100%;
    background-repeat: no-repeat;
    margin: 0;
    padding: 100px;
    box-sizing: border-box;
}

.NAV {
    /* padding-top: 100px; */
    background-color: whitesmoke;
    width: 700px;
    height: 550px;
    margin: 0 100px;
}

.nav3 {
    width: 700px;
    height: 100px;
}